Micromechanical phase-shifting gate optical modulator

Abstract

A micromechanical optical modulator includes an input optical waveguide that projects a beam across a gap to an output optical waveguide. A phase shifting gate is mounted between the input and output optical waveguides and has a light transmissive panel which may have at least two sections of different thicknesses. The phase shifting gate is translatable between a position in which the beam of light is transmitted and a second position in which a section of the gate panel is interposed in the beam path and the beam of light is reflected by interference effects. A micromechanical actuator may be connected to the phase shifting gate to switch it between its positions. The optical waveguides may be mounted at an angle to the surfaces of the sections of the gate such that when the beam is reflected from the gate it is directed to a second output optical waveguide, which receives the beam and directs it on a new path, thereby allowing switching of optical beam paths in an optical communication system. The optical modulator may also be used as a sensor to detect effects which displace the phase shifting gate, such as in an accelerometer in which a mass is connected to the gate to move the gate when the mass is subjected to accelerations.

What is claimed is:  
     
       1. A micromechanical optical modulator comprising: 
       (a) an input optical waveguide with an exit face from which a light beam can exit the waveguide;  
       (b) an output optical waveguide with an entrance face spaced from the exit face of the input optical waveguide to receive a light beam exiting from the exit face of the input optical waveguide on a beam path; and  
       (c) a phase shifting gate mounted between the input optical waveguide and output optical waveguide, the phase shifting gate having a light transmissive panel having at least one section having outer surfaces, the phase shifting gate translatable between at least two positions, wherein in one of the positions of the gate the beam is transmitted from the input optical waveguide on the beam path to the output optical waveguide, and in the other position of the gate, the panel section is interposed in the beam path from the input optical waveguide to the output optical waveguide, wherein the spacing between the exit face of the input optical waveguide and the adjacent outer surface of the section of the light transmissive panel, the spacing between the entrance face of the output optical waveguide and the adjacent outer surface of the section of the light transmissive panel, and the index of refraction of the light transmissive panel are selected for a selected wavelength of light in a beam exiting from the exit face of the input optical waveguide such that in the position of the phase shifting gate in which the section of the light transmissive panel is interposed in the beam path, the light in the beam is substantially reflected by interference effects.  
     
     
       2. The optical modulator of  claim 1  wherein the light transmissive panel of the gate is formed of silicon. 
     
     
       3. The optical modulator of  claim 2  wherein the wavelength of light in the beam exiting from the exit face of the input waveguide is centered at 1.55 μm. 
     
     
       4. The optical modulator of  claim 1  wherein in the position of the gate in which the light beam is transmitted on the beam path from the input optical waveguide to the output optical waveguide, the gate panel is out of the beam path. 
     
     
       5. The optical modulator of  claim 1  wherein the input and output optical waveguides comprise optical fibers. 
     
     
       6. The optical modulator of  claim 1  wherein the phase shifting gate has a light transmissive panel having at least two sections having outer surfaces, one thicker section having a thickness greater than that of another thinner section, wherein in one of the positions of the gate the thinner section of the light transmissive panel is interposed in the beam path between the input optical waveguide and the output optical waveguide and in the other position of the gate the thicker section is interposed in the beam path from the input optical waveguide to the output optical waveguide, wherein the spacing between the exit face of the input optical waveguide and the adjacent outer surfaces of the light transmissive panel in the thicker and thinner sections, the spacing between the entrance face of the output optical waveguide and the adjacent outer surfaces of the thicker and thinner sections of the light transmissive panel, and the index of refraction of the light transmissive panel are selected for a selected wavelength of light in a beam exiting from the exit face of the input optical waveguide such that in one of the positions of the phase shifting gate the beam is transmitted through the light transmissive panel and in a second position of the gate, the light in the beam is substantially reflected by interference effects. 
     
     
       7. The optical modulator of  claim 6  wherein there are at least two input optical waveguides and at least two output optical waveguides, each output optical waveguide paired with an input optical waveguide such that a beam is directed on a beam path from an exit face of each input optical waveguide to an entrance face of an output optical waveguide that is spaced therefrom, wherein in one of the positions of the phase shifting gate the thicker section of the light transmissive panel is in the beam path between one of the pairs of input and output optical waveguides and the thinner section of the light transmissive panel is in the beam path between another of the pairs of input and output optical waveguides, and wherein the thicknesses of the sections between the pairs of optical waveguides is switched in the other position of the gate. 
     
     
       8. The optical modulator of  claim 7  wherein the pairs of input and output waveguides are arranged such that the beam paths between the pairs of optical waveguides are parallel to one another, and wherein the phase shifting gate is mounted for translation perpendicularly to the beam paths between the pairs of optical waveguides, and wherein, in one position of the gate, the beam is transmitted through the gate panel between a first of the pairs of input and output optical waveguides and the beam between the second of the pairs of optical waveguides is reflected by interference effects and wherein, in the other position of the gate, the beam between the second of the pairs of optical waveguides is transmitted through the gate panel and the beam between the first pair of optical waveguides is reflected by interference effects. 
     
     
       9. The optical modulator of  claim 8  wherein the light transmissive panel of the phase shifting gate is formed of silicon and including an interface plate formed of silicon secured to the exit faces of the input optical waveguides and an interface plate formed by silicon secured to the entrance faces of the output optical waveguides. 
     
     
       10. The optical modulator of  claim 6  wherein there are at least two input optical waveguides and at least two output optical waveguides, each output optical waveguide paired with an input optical waveguide such that a beam is directed on a beam path from an exit face of each input optical waveguide to an entrance face of an output optical waveguide that is spaced therefrom, the pairs of input and output optical waveguides arranged such that the beam paths between the two pairs of optical waveguides are diagonal to and cross each other, and wherein in one of the positions of the phase shifting gate the thicker section of the light transmissive panel is in the beam paths between the pairs of input and output optical waveguides in the other of the positions of the gate the thinner section of the light transmissive panel is in the beam paths between the pairs of input and output optical waveguides. 
     
     
       11. The optical modulator of  claim 6  wherein the phase shifting gate is mounted for translation perpendicularly to the beam path from the exit face of the input optical waveguide to the entrance face of the output optical waveguide, and wherein the surfaces of the thicker section and the thinner section of the light transmissive panel of the phase shifting gate are parallel to one another and to the exit face and to the entrance face, and wherein in a first position of the gate wherein one of the sections is in the beam path, for a beam having a selected wavelength X 0 , the spacing between the entrance face and the surface of the panel section adjacent to it and the spacing between the entrance face and the surface of the panel section adjacent to it are selected to be odd multiples of λ 0 /4n air , and the thickness of the one section between its surface is selected to be an odd multiple of λ 0 /4n g  to obtain maximum reflectivity, where n air  is the index of refraction of air and n g  is the index of the refraction of the material of the transmissive panel, and in the other position of the gate the thickness of the other section of the gate between its surfaces which is now in the beam between the exit face and the entrance face is selected to be an even multiple of λ 0 /4n g  to obtain minimum reflectivity and maximum transmission through the gate. 
     
     
       12. The optical modulator of  claim 11  wherein the light transmissive panel of the gate is formed of silicon. 
     
     
       13. The optical modulator of  claim 1  further including a micromechanical actuator connected to the gate to drive the gate between its at least two positions. 
     
     
       14. The optical modulator of  claim 13  further including a micromechanical spring mounted to a substrate and connected to the phase shifting gate to support the gate for lateral translation between its positions above the substrate. 
     
     
       15. The optical modulator of  claim 13  wherein the actuator comprises interdigitated comb elements, one set of comb elements connected to the gate and the other set of comb elements mounted to a substrate such that a voltage applied to one of the sets of comb elements will draw the comb elements together to drive the gate. 
     
     
       16. The optical modulator of  claim 1  wherein the spacing between the exit face of the input optical waveguide and the entrance face of the output optical waveguide is less than 1 mm. 
     
     
       17. The optical modulator of  claim 16  wherein the spacing between the exit face and the entrance face is less than 40 μm. 
     
     
       18. The optical modulator of  claim 1  wherein the light transmissive panel of the phase shifting gate is formed of silicon and including an interface plate formed of silicon secured to the exit face of the input waveguide and an interface plate of silicon secured to the entrance face of the output waveguide. 
     
     
       19. The optical modulator of  claim 1  further including a proof mass connected to the phase shifting gate and a support spring connected to the phase shifting gate to support the gate for lateral motion and to bias the gate back to a normal position, such that the proof mass will displace the phase shifting gate in response to acceleration. 
     
     
       20. The optical modulator of  claim 1  including micromechanical clips formed on a substrate into which the input optical waveguide and the output optical waveguide are inserted to hold them in place. 
     
     
       21. A micromechanical optical modulator switch comprising: 
       (a) two input optical waveguides each with an exit face from which a light beam can exit the waveguide;  
       (b) two output optical waveguides each with an entrance face spaced from an exit face of one of the input optical waveguides to receive a light beam exiting from the exit face of the input optical waveguide on a beam path to define two pairs of input and output optical waveguides, wherein the pairs of input and output optical waveguides are arranged such that the beam paths between the two pairs of optical waveguides are diagonal to and cross each other;  
       (c) a phase shifting gate mounted between the input optical waveguides and the output optical waveguides, the phase shifting gate having a light transmissive panel having at least one section having outer surfaces, the phase shifting gate translatable between at least two positions, wherein in one of the positions of the gate the beams are transmitted on the beam paths between each pair of input and output optical waveguides, and in the other position of the gate the one section is interposed in the beam paths between the pairs of optical waveguides, wherein the spacing between the exit faces of the input optical waveguides and the adjacent surface of the section of the light transmissive panel, the spacing between the entrance faces of the output optical waveguides and the adjacent surfaces of the section of the light transmissive panel, and the index of refraction of the light transmissive panel are selected for a selected wavelength of light in the beam exiting from the exit faces of the input optical waveguides such that in the position of the phase shifting gate in which the panel section is interposed in the beam paths, the light in the beams between the pairs of optical waveguides is substantially reflected by interference effects; and  
       (d) a micromechanical actuator connected to the gate to drive the gate between its at least two positions.  
     
     
       22. The optical modulator switch of  claim 21  wherein in the position of the gate in which the light in the beams is reflected, the beam from the input optical waveguide in a first pair of optical waveguides is reflected to and is received by the entrance face of the output optical waveguide in the second of the pairs of optical waveguides, and the beam from the input optical waveguide in the second of the pairs of optical waveguides is reflected to and is received by the entrance face of the output optical waveguide in the first of the pairs of optical waveguides. 
     
     
       23. The optical modulator switch of  claim 21  wherein the light transmissive panel of the gate is formed of silicon. 
     
     
       24. The optical modulator switch of  claim 23  wherein the wavelength of light in the beams exiting from the exit faces of the input waveguides is centered at 1.55 μm. 
     
     
       25. The optical modulator switch of  claim 21  further including a micromechanical spring mounted to a substrate and connected to the phase shifting gate to support the gate for lateral translation between its positions above the substrate. 
     
     
       26. The optical modulator switch of  claim 25  wherein the actuator comprises interdigitated comb elements, one set of comb elements connected to the gate and the other set of comb elements mounted to a substrate such that a voltage applied to one of the sets of comb elements will draw the comb elements together to drive the gate. 
     
     
       27. The optical modulator switch of  claim 21  wherein the spacing between the exit face of the input optical waveguide in each pair and the entrance face of the output optical waveguide in each pair is less than 1 mm. 
     
     
       28. The optical modulator switch of  claim 27  wherein the spacing between the exit face and the entrance face of the optical waveguides in each pair is less than 40 μm. 
     
     
       29. The optical modulator switch of  claim 21  wherein the input and output optical waveguides comprise optical fibers. 
     
     
       30. The optical modulator switch of  claim 21  wherein in the position of the gate panel in which the light beams are transmitted on the beam paths between the pairs of input and output waveguides, the gate panel is out of the beam paths. 
     
     
       31. The optical modulator switch of  claim 21  wherein the phase shifting gate has a light transmissive panel having at least two sections having outer surfaces, at least one thicker section having a thickness greater than that of at least one other thinner section, wherein in one of the positions of the gate a thinner section of the light transmissive panel is interposed in the beam paths between the pairs of optical waveguides, and in the other position of the gate a thicker section is interposed in the beam paths between the pairs of optical waveguides, wherein the spacing between the exit faces of the input optical waveguides and the adjacent surfaces of the light transmissive panel in the thicker and thinner sections, the spacing between the entrance faces of the output optical waveguides and the adjacent surfaces of the thicker and thinner sections of the light transmissive panel, and the index of refraction of the light transmissive panel are selected for a selected wavelength of light in the beam exiting from the exit faces of the input optical waveguides such that in one of the positions of the phase shifting gate the beams between each pair of optical waveguides are transmitted through the light transmissive panel, and in a second position of the gate the light in the beams between the pairs of optical waveguides is substantially reflected by interference effects. 
     
     
       32. A micromechanical optical modulator comprising: 
       (a) an input optical waveguide with an exit face from which a light beam can exit the waveguide;  
       (b) an output optical waveguide with an entrance face, the output optical waveguide mounted adjacent to the input optical waveguide;  
       (c) a plate of light transmissive material mounted to receive a light beam exiting from the exit face of the input optical waveguide;  
       (d) a phase shifting gate mounted between the input and output optical waveguides and the plate, the phase shifting gate having a light transmissive panel having at least one section having outer surfaces, the phase shifting gate translatable between at least two positions, wherein in one of the positions of the gate the beam from the input optical waveguide is transmitted to the plate, and wherein in the other position of the gate the panel section is interposed in the beam path from the input optical waveguide to the plate, wherein the spacing between the exit face of the input optical waveguide and the adjacent outer surface of the section of the light transmissive panel, the spacing between the plate and the adjacent outer surface of the section of the light transmissive panel, and the index of refraction of the light transmissive panel are selected for a selected wavelength of light in a beam exiting from the exit face of the input optical waveguide such that in the position of the phase shifting gate in which the one section of the light transmissive panel is interposed in the beam path gate, the light in the beam is substantially reflected by interference effects to the entrance face of the output optical waveguide.  
     
     
       33. The optical modulator of  claim 32  wherein the phase shifting gate has a light transmissive panel having at least two sections having outer surfaces, one thicker section having a thickness greater than that of another thinner section, wherein in one of the positions of the gate the thinner section of the light transmissive panel is interposed in the beam path between the input optical waveguide and the output optical waveguide and in the other position of the gate the thicker section is interposed in the beam path from the input optical waveguide to the output optical waveguide, wherein the spacing between the exit face of the input optical waveguide and the adjacent outer surfaces of the light transmissive panel in the thicker and thinner sections, the spacing between the light transmissive plate of the output and the adjacent outer surfaces of the thicker and thinner sections of the light transmissive panel, and the index of refraction of the light transmissive panel are selected for a selected wavelength of light in a beam exiting from the exit face of the input optical waveguide such that in one of the positions of the phase shifting gate the beam is transmitted through the light transmissive panel and in a second position of the gate, the light in the beam is substantially reflected by interference effects. 
     
     
       34. The optical modulator of  claim 32  wherein the light transmissive panel of the gate and the light transmissive plate are formed of silicon. 
     
     
       35. A micromechanical optical modulator comprising: 
       (a) an input optical waveguide with an exit face from which a light beam can exit the waveguide;  
       (b) a plate of light transmissive material with a surface spaced from the exit face of the input optical waveguide to receive a light beam exiting from the exit face of the input optical waveguide on a beam path; and  
       (c) a phase shifting gate mounted between the input optical waveguide and the light transmissive plate, the phase shifting gate having a light transmissive panel having at least one section having outer surfaces, the phase shifting gate translatable between at least two positions, wherein in one of the positions of the gate the beam from the input optical waveguide is transmitted to the plate, and wherein in the other position of the gate the section is interposed in the beam path from the input optical waveguide to the plate, wherein the spacing between the exit face of the input optical waveguide and the adjacent outer surface of the section of the light transmissive panel, the spacing between the plate and the adjacent outer surface of the section of the light transmissive panel, and the index of refraction of the light transmissive panel are selected for a selected wavelength of light in a beam exiting from the exit face of the input optical waveguide such that in the position of the phase shifting gate in which the section of the light transmissive panel is interposed in the beam path, the light in the beam is substantially reflected by interference effects back to the exit face of the input optical waveguide.  
     
     
       36. The optical modulator of  claim 35  wherein the phase shifting gate has a light transmissive panel having at least two sections having outer surfaces, one thicker section having a thickness greater than that of another thinner section, wherein in one of the positions of the gate the thinner section of the light transmissive panel is interposed in the beam path and in the other position of the gate the thicker section is interposed in the beam path, wherein the spacing between the exit face of the input optical waveguide and the adjacent outer surfaces of the light transmissive panel in the thicker and thinner sections, the spacing between the plate of light transmissive material and the adjacent outer surfaces of the thicker and thinner sections of the light transmissive panel, and the index of refraction of the light transmissive panel are selected for a selected wavelength of light in a beam exiting from the exit face of the input optical waveguide such that in one of the positions of the phase shifting gate the beam is transmitted through the light transmissive panel and in a second position of the gate, the light in the beam is substantially reflected by interference effects. 
     
     
       37. The optical modulator of  claim 35  wherein the light transmissive panel of the gate is formed of silicon. 
     
     
       38. A micromechanical optical modulator accelerometer comprising: 
       (a) an input optical waveguide with an exit face from which a light beam can exit the waveguide;  
       (b) an output optical waveguide with an entrance face spaced from the exit face of the input optical waveguide to receive a light beam exiting from the exit face of the input optical waveguide on a beam path;  
       (c) a phase shifting gate mounted between the input optical waveguide and output optical waveguide, the phase shifting gate having a light transmissive panel having at least one section having outer surfaces, the phase shifting gate translatable between at least two positions, wherein in one of the positions of the gate the beam from the input optical waveguide is transmitted to the output optical waveguide, and wherein in the other position of the gate the section is interposed in the beam path from the input optical waveguide to the output optical waveguide, wherein the spacing between the exit face of the input optical waveguide and the adjacent outer surface of the section of the light transmissive panel, the spacing between the entrance face of the output optical waveguide and the adjacent outer surface of the section of the light transmissive panel, and the index of refraction of the light transmissive panel are selected for a selected wavelength of light in a beam exiting from the exit face of the input optical waveguide such that in the one position of the phase shifting gate in which the section of the light transmissive panel is interposed in the beam path, the light in the beam is substantially reflected by interference effects;  
       (d) a proof mass connected to the phase shifting gate; and  
       (e) a support spring connected to the phase shifting gate to support the gate for lateral motion and to bias the gate back to a normal position, such that the proof mass will displace the phase shifting gate in response to acceleration.  
     
     
       39. The optical modulator accelerator of  claim 38  wherein the phase shifting gate has a light transmissive panel having at least two sections having outer surfaces, one thicker section having a thickness greater than that of another thinner section, wherein in one of the positions of the gate the thinner section of the light transmissive panel is interposed in the beam path between the input optical waveguide and the output optical waveguide and in the other position of the gate the thicker section is interposed in the beam path from the input optical waveguide to the output optical waveguide, wherein the spacing between the exit face of the input optical waveguide and the adjacent outer surfaces of the light transmissive panel in the thicker and thinner sections, the spacing between the entrance face of the output optical waveguide and the adjacent outer surfaces of the thicker and thinner sections of the light transmissive panel, and the index of refraction of the light transmissive panel are selected for a selected wavelength of light in a beam exiting from the exit face of the input optical waveguide such that in one of the positions of the phase shifting gate the beam is transmitted through the light transmissive panel and in a second position of the gate, the light in the beam is substantially reflected by interference effects. 
     
     
       40. The optical modulator accelerometer of  claim 39  wherein the phase shifting gate is mounted for translation perpendicularly to the beam path from the exit face of the input optical waveguide to the entrance face of the output optical waveguide, and wherein the surfaces of the thicker section and the thinner section of the light transmissive panel of the phase shifting gate are parallel to one another and to the exit face and to the entrance face, and wherein in a first position of the gate wherein one of the sections is in the beam path, for a beam having a selected wavelength λ 0 , the spacing between the entrance face and the surface of the panel section adjacent to it and the spacing between the entrance face and the surface of the panel section adjacent to it are selected to be odd multiples of λ 0 /4n air , and the thickness of the one section between its surface is selected to be an odd multiple of λ 0 /4n g  to obtain maximum reflectivity, where n air  is the index of refraction air and n g  is the index of the refraction material of the transmissive panel, and in the other position of the gate the thickness of the other section of the gate between its surfaces which is now in the beam between the exit face and the entrance face is selected to be an even multiple of λ 0 /4n g  to obtain minimum reflectivity and maximum transmission through the gate. 
     
     
       41. The optical modulator accelerometer of  claim 40  wherein the light transmissive panel of the gate is formed of silicon. 
     
     
       42. The optical modulator accelerometer of  claim 38  wherein the light transmissive panel of the gate is formed of silicon. 
     
     
       43. The optical modulator accelerometer of  claim 42  wherein the wavelength of light in the beam exiting from the exit face of the input waveguide is centered at 1.55 μm. 
     
     
       44. The optical modulator accelerometer of  claim 38  wherein the spacing between the exit face of the input optical waveguide and the entrance face of the output optical waveguide is less than 1 mm. 
     
     
       45. The optical modulator accelerometer of  claim 44  wherein the spacing between the exit face and the entrance face is less than 40 μm. 
     
     
       46. The optical modulator accelerometer of  claim 38  wherein the light transmissive panel of the phase shifting gate is formed of silicon and including an interface plate formed of silicon secured to the exit face of the input waveguide and an interface plate of silicon secured to the entrance face of the output waveguide. 
     
     
       47. A method of modulating light in a light beam comprising: 
       (a) projecting light from an exit face of an input optical waveguide in a beam toward an entrance face of an output optical waveguide;  
       (b) interposing a first section of a panel of light transmissive material in the beam, the panel section having a selected thickness to transmit the light beam through the section to the entrance face of the output optical waveguide; and  
       (c) interposing a second section of a panel of light transmissive material in the beam, the thickness of the second section, the index of refraction of the second section, and the spacing of surfaces of the second section from the exit face of the input optical waveguide and the entrance face of the output optical waveguide selected so as to reflect the light in the beam by interference effects.  
     
     
       48. The method of  claim 47  wherein the sections of the panel interposed in the beam are part of a unitary panel having a first section of a first thickness between the surfaces of the section and a second adjacent section of a second greater thickness between the surfaces of the section of the panel, and wherein in the step of interposing a first section in the beam at a selected thickness to transmit the light beam the panel is translated to a position so that a first of the sections of the panel is in the beam and, in the step of interposing a panel in the beam to reflect the light, the panel is translated laterally to another position to bring the second of the sections of the panel into the beam. 
     
     
       49. The method of  claim 48  wherein in the step of projecting light from the exit face of the input optical waveguide the light is projected at a wavelength centered at 1.55 μm, and wherein the panel is formed of silicon. 
     
     
       50. The method of  claim 49  wherein the input optical waveguide and the output optical waveguide constitute a first input optical waveguide and a first output optical waveguide, and further including, projecting light from an exit face of a second input optical waveguide in a beam toward an entrance face of a second output optical waveguide, and wherein the panel of light transmissive material is interposed in the beam path between the second input optical waveguide and second output optical waveguide through a section of the panel of a different thickness than the thickness of the section of the panel through which light is projected from the first input optical waveguide to the first output optical waveguide. 
     
     
       51. A method of modulating a beam of light to switch the beam of light comprising: 
       (a) projecting light from an exit face of a first input optical waveguide in a beam toward the entrance face of a first output optical waveguide;  
       (b) providing a panel of material that is transmissive to the beam of light, the panel having at least two sections of two different thicknesses, and interposing a one of the sections of the panel in the beam between the exit face and the entrance face that is selected to transmit the beam through the section of the panel from the exit face of the input optical waveguide to the entrance face of the output optical waveguide;  
       (c) then interposing the second of the sections of the panel in the beam between the exit face of the first input optical waveguide and the first output optical waveguide, the second of the sections selected in thickness, index of refraction, and spacing from the exit face of the first input optical waveguide and the entrance face of the first output optical waveguide such that the beam is reflected by interference effects, and reflecting the beam to and receiving the beam by an entrance face of a second output optical waveguide to transmit the beam on the second output optical waveguide.  
     
     
       52. The method of  claim 51  including providing a second input optical waveguide and projecting light from an exit face of the second input optical waveguide in a beam toward the entrance face of the second output optical waveguide, and wherein when the section of the panel is in the position to transmit the beam from the first input optical waveguide to the first output optical waveguide, the beam projected from the exit face of the second input optical waveguide is transmitted through the panel to and is received by the entrance face of the second output optical waveguide, and 
       when the panel is in the position with the section of the panel reflecting light in the beam projected from the exit face of the first input optical waveguide the panel reflects the beam projected from the exit face of the second input optical waveguide and reflects the beam to the entrance face of the first output optical waveguide.  
     
     
       53. The method of  claim 52  wherein the light transmissive panel is formed of silicon and the beam is projected from the exit face of the first input optical waveguide at a wavelength centered at 1.55 μm. 
     
     
       54. A method of modulating light in a light beam comprising: 
       (a) projecting light from an exit face of an input optical waveguide in a beam toward an entrance face of a light transmissive material,  
       (b) transmitting the light beam from the exit face to the entrance face; and  
       (c) interposing a section of a panel of light transmissive material in the beam, the thickness of the section, the index of refraction of the section, and the spacing of surfaces of the section from the exit face of the input optical waveguide and from the entrance face selected so as to reflect the light in the beam by interference effects.  
     
     
       55. The method of  claim 54  wherein the section of the panel interposed in the beam is part of a unitary panel having a first section of a first thickness between the surfaces of the section and a second adjacent section of a second greater thickness between the surfaces of the section of the panel, and including the steps of interposing a first section in the beam at a selected thickness to transmit the light beam through the first section by translating the panel to a position in which the first of the sections of the panel is in the beam and, in the step of interposing a panel in the beam to reflect the light, the panel is translated laterally to another position to bring the second of the sections of the panel into the beam. 
     
     
       56. The method of  claim 55  wherein in the step of projecting light from the exit face of the input optical waveguide the light is projected at a wavelength centered at 1.55 μm, and wherein the panel is formed of silicon.